1. Field of the Invention
This invention relates to the method and apparatus for controlling the operation of electric power generating plants of a system to meet economically the forecast of system loads, and in particular, to the coordination of a multiplicity of hydro and thermal generating units within a single system.
2. Description of the Prior Art
The operating procedure of electric companies using both hydro and thermal generating units has traditionally been the manual scheduling of system generation based upon "peak-shaving" with the hydroelectric generating units. All pre-scheduling was based upon the operator's projection of future system needs and available resources. In some cases, the plan of solution was an iterative cost trajectory optimization. In this method, a feasible commitment of units is input to a computer program and then a classical hydro-thermal coordination is conducted using the input commitment. After obtaining a satisfactory water balance for the scheduling day, the start-stop times of both hydro and thermal units are varied until no further savings are gained. However, such a method for achieving unit commitment and economic dispatch required long computation times.
In order to expedite the solution of hydrothermal coordination, logical scheduling rules employed by a power company from its experience are used to obtain a sub-optimal solution to the commitment problem. This solution provides an initial schedule. By means of computer simulation, both large and small variations are made to the initial commitment to obtain a less costly daily commitment. For this optimized schedule, transmission loss penalty factors are calculated and used in interchange negotiations and for subsequent running of the dispatch program.
Selected hydro units are scheduled by a technique known as "peak shaving". The schedule for the remainder of the hydro units is input. For pumped hydro units, either the initial pump-generate schedule may be input of the pump schedule only may be input with the generation determined by peak shaving. Selected hydro and thermal units are committed to non-spin status for satisfaction of the five-minute reserve requirements. Selected hydro units are placed on motor status to contribute toward the five-minute reserves. The on-line hydro-system five and thirty-minute reserves are calculated. The hydro scheduling logic of peak shaving involves scheduling hydro energy for generation during high load hours. A magnitude ordered load versus time curve is contructed and hydro energy is successively removed from the high to low load hours until all hydro energy specified for a given unit is used.
Computation for hydro optimization attempts to decrease cost by increasing hydro generation in certain hours and decreasing hydro generation in other hours. The test of where to shift hydro is related to the value of system incremental cost for all hours. High lambda hours in which no hydro is used, are potential hours of tentative hydro swap with lower lambda hours in which hydro is used. Dispatching, costing and testing of actual savings comprise the major elements of computation.
Constructions of mathematical models of hydrothermal systems showed that the classical approach would result in an unwieldly number of parameters for which the solution time would be impractical on an on-line digital control computer. Based on the geographical separation of the hydro-electric and thermal generation sub-systems, a modeling technique is suggested by this invention which utilizes this isolation. As is evident in the description of this invention herein, the two sub-systems, hydro and thermal, are dispatched separately with system convergence dependent upon the iteration between the two sub-systems. In contrast, classical methods would dictate a gamma, where gamma is an artificial cost of water in terms of dollars per acre-foot, for each hydro plant, thus, presenting a large number of parameters for solution. No representation is made that any prior art considered herein is the best pertaining prior art nor that the considered prior art cannot be interpreted differently from the interpretations placed on it herein.